Project Summary The long term goal of this study is to understand how biological membranes control their structural integrity, dynamical response, and physiological performance. Here we specifically study the erythrocyte membrane which has a protein network coupled to a lipid bilayer. We recently developed a new molecular-based hybrid model for the 3D dynamic response of this coupled structure. The model incorporates a 3D configuration of the junctional complex we predicted, the network topology revealed by transmission electron microscopy, and several interactions between the protein network and the lipid bilayer reported in literatures. By extending this 3D dynamic model, specific aims are proposed to test and model diseased erythrocyte membrane mechanics. The multiple- scale modeling will include the molecular-based hybrid model and a complete cell model with a Finite-Element Method. Models will be tested against published data on mutant human erythrocytes (e.g. hemolytic spherocytosis and elliptocytosis) and new data to be obtained for knockout mouse cells. Experiments will include micropipette aspiration, quasi-static and rate dependent testing and viscoelastic constitutive response with novel microrheology methods. The viscoelasticity will be compared with the molecular-based hybrid model, while the deformation of the cell will be compared with the complete cell model. This work will shed new light into physiological mechanisms by which diffusion/transport, structural sustainability, and signal transduction may be further regulated by the dynamics of the elements in the network at the nano-scale. This knowledge may provide the missing link between molecular organization and biomechanics of the membrane, and improve the understanding and treatment of hematological disorders. The broader impact is a framework to understand a wide class of interesting and important biological membrane structures and paths for biomimetics in synthetic bio-membranes, membrane-based bio-sensors, and other structures. Project Narrative: The proposed research will allow us to understand how the three-dimensional molecular organization of the red blood cell membrane provides structural sustainability of the cells and facilitates the diffusion/transport of oxygen and carbon dioxide during circulation. This study will also help us understand how genetic defects in the membrane structure may result in shorter life of red blood cells in hematological disorders. It will also lay a foundation for scientists and engineers to build biologically-inspired structures.